Patch by Thomas Thurman <tthurman@gnome.org> which adds a new command-line switch
to metacity: --ignore-screens=<int>{,<int>{,...}} to tell metacity to avoid
management of certain screens. For example, --ignore-screens=1 will tell metacity
to not manage screens :?,1 (where ? is any number).

Original patch here:
http://bugzilla.gnome.org/show_bug.cgi?id=351647

diff -ur metacity-2.26.0.orig/src/core/display.c metacity-2.26.0/src/core/display.c
--- metacity-2.26.0.orig/src/core/display.c	2009-06-24 22:29:59.000000000 +0400
+++ metacity-2.26.0/src/core/display.c	2009-06-24 22:57:21.000000000 +0400
@@ -31,6 +31,7 @@
  */
 
 #include <config.h>
+#include <stdlib.h>
 #include "display-private.h"
 #include "util.h"
 #include "main.h"
@@ -309,7 +310,7 @@
  * \ingroup main
  */
 gboolean
-meta_display_open (void)
+meta_display_open (gchar *screens_not_to_handle)
 {
   Display *xdisplay;
   GSList *screens;
@@ -693,16 +694,34 @@
   
   screens = NULL;
   
-  i = 0;
-  while (i < ScreenCount (xdisplay))
+  for (i=0; i < ScreenCount (xdisplay); i++)
     {
-      MetaScreen *screen;
+      char *dont_handle_cursor =
+        screens_not_to_handle? screens_not_to_handle: "";
+      gboolean handle_this_screen = TRUE;
 
-      screen = meta_screen_new (the_display, i, timestamp);
+      while (*dont_handle_cursor)
+        {
+          while (*dont_handle_cursor!=0 &&
+                 *dont_handle_cursor!='-' &&
+                 (*dont_handle_cursor<'0' || *dont_handle_cursor>'9'))
+            dont_handle_cursor++; /* skip separators */
 
-      if (screen)
-        screens = g_slist_prepend (screens, screen);
-      ++i;
+          if (*dont_handle_cursor &&
+              strtol (dont_handle_cursor, &dont_handle_cursor, 10) == i)
+            {
+              handle_this_screen = FALSE;
+              break;
+            }
+        }
+
+      if (handle_this_screen)
+        {
+          MetaScreen *screen = meta_screen_new (the_display, i, timestamp);
+
+          if (screen)
+            screens = g_slist_prepend (screens, screen);
+        }
     }
   
   the_display->screens = screens;
@@ -712,6 +731,8 @@
       /* This would typically happen because all the screens already
        * have window managers.
        */
+      meta_warning (_("Cannot start because all available screens were "
+                      "either unavailable or ignored.\n"));
       meta_display_close (the_display, timestamp);
       return FALSE;
     }
diff -ur metacity-2.26.0.orig/src/core/display-private.h metacity-2.26.0/src/core/display-private.h
--- metacity-2.26.0.orig/src/core/display-private.h	2009-02-05 04:10:05.000000000 +0300
+++ metacity-2.26.0/src/core/display-private.h	2009-06-24 22:57:21.000000000 +0400
@@ -319,7 +319,7 @@
      (time2) != 0)                                                      \
   )
 
-gboolean      meta_display_open                (void);
+gboolean      meta_display_open                (gchar *screens_not_to_handle);
 void          meta_display_close               (MetaDisplay *display,
                                                 guint32      timestamp);
 MetaScreen*   meta_display_screen_for_x_screen (MetaDisplay *display,
diff -ur metacity-2.26.0.orig/src/core/main.c metacity-2.26.0/src/core/main.c
--- metacity-2.26.0.orig/src/core/main.c	2009-02-05 04:10:05.000000000 +0300
+++ metacity-2.26.0/src/core/main.c	2009-06-24 23:06:38.000000000 +0400
@@ -219,6 +219,7 @@
   gboolean sync;
   gboolean composite;
   gboolean no_composite;
+  gchar *ignore_screens;
 } MetaArguments;
 
 #ifdef HAVE_COMPOSITE_EXTENSIONS
@@ -245,7 +246,7 @@
                     MetaArguments *meta_args)
 {
   MetaArguments my_args = {NULL, NULL, NULL,
-                           FALSE, FALSE, FALSE, FALSE, FALSE};
+                           FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, NULL};
   GOptionEntry options[] = {
     {
       "sm-disable", 0, 0, G_OPTION_ARG_NONE,
@@ -300,6 +301,12 @@
       N_("Turn compositing off"),
       NULL
     },
+    {
+      "ignore-screens", 'S', 0, G_OPTION_ARG_STRING,
+      &my_args.ignore_screens,
+      N_("Comma-separated list of screens to ignore"),
+      NULL
+    },
     {NULL}
   };
   GOptionContext *ctx;
@@ -526,9 +533,11 @@
   if (meta_args.composite || meta_args.no_composite)
     meta_prefs_set_compositing_manager (meta_args.composite);
 
-  if (!meta_display_open ())
+  if (!meta_display_open (meta_args.ignore_screens))
     meta_exit (META_EXIT_ERROR);
-  
+
+  g_free (meta_args.ignore_screens);
+
   g_main_loop_run (meta_main_loop);
 
   meta_finalize ();